Habitat, Survival, Productivity, and Abundance of Pheasants in Western Oregon, 1947-1975

Abstract

Indices of survival, productivity, and density were derived from annual censuses of ringnecked pheasants (Phasianus colchicus) in the Willamette Valley from 1947 to 1975. Abundance of pheasants in spring was moderate and variable in the late 1940's and early 1950's (10-20 birds/40.5 ha), increased in the early 1960's (35-40/40.5 ha), and decreased in the early 1970's (3-8/40.5 ha). Amount of land in soil bank was closely correlated to abundance of pheasants in spring. Reproductive performance remained relatively constant from 1949 to 1975. Survival of adult females during summer and during winter were significantly correlated (r = 0.89) to annual percent change in total density of pheasants in spring. About 25 to 30 percent of the pheasant habitat in the Willamette Valley was lost between 1945 and 1970. Survival of adult females was the most important factor affecting long term trends in population size. J. WILDL. MANAGE. 42(4):866-874 Populations of ring-necked pheasants have undergone many changes since the introduction of the species in the Willamette Valley, Oregon, in 1881 (Gabrielson and Jewett 1970:226). Of particular interest is the recent (-10 years) decline in abundance experienced by many populations of pheasants (Leite 1971, Tripp 1971, Nish 1973, Snyder 1973, Weigand 1973, Labisky 1975). The pheasant population in the Willamette Valley was no exception, declining to very low levels in the early 1970's. Most of the declines were attributed to changes in quantity and quality of habitat but the relationships between habitat and population dynamics were not specified. The interest of wildlife managers in predicting fall population levels generated many investigations of the causes of annual changes in population levels. Some of the factors reported to influence fall population levels included weather in spring and winter, number of young produced, number of females in spring, survival of females, and behavior of chicks and nesting females (Green 1938, Allen 1950, Kozicky and Hendrickson 1951, Stokes 1954, Linder and Agee 1965, Wagner et al. 1965, Stokes 1968, Wagner and Stokes 1968, Gates and Hale 1975). However, none of these factors fully explains long-term changes in abundance of pheasants. Our objectives were to determine the relative importance of survival and recruitment to long-term changes in abundance of pheasants and to relate changes in quantity and quality of habitat to recruitment, survival, and abundance. W. L. Allen, Benton County Office, Agricultural Stabilization and Conservation Service assisted in obtaining aerial photographs, and F. Ives, Oregon Department of Fish and Wildlife, provided data and field notes of pheasant censuses. E. C. Meslow and J. A. Crawford reviewed the manuscript.